Fort Leaton State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Leaton State Historic Site clear sky chart from 2005-11-06 to 2025-12-18.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	3 2 1 3 2 3 3 3 5% 7% 68%	134551
	Night	3 3 1 3 3 3 4 3 5% 8% 64%	133890
Transparency	Day	9% 38% 5% 13% 17% 18%	129663
	Night	11% 38% 5% 11% 16% 18%	129781
Seeing	Day	4 4 13% 32% 30% 17%	15543
	Night	5% 3 22% 49% 20% 1	26020

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	3 2 1 3 2 2 3 2 5% 8% 70%	4537
	11th to 20th	Day	3 2 1 2 2 2 2 3 4 6% 74%	4540
	21st to end	Day	3 4 1 4 3 3 4 2 4 6% 65%	4994
February	1st to 10th	Day	3 3 1 4 3 3 4 4 5% 6% 64%	2000
	11th to 20th	Day	4 4 1 4 3 3 3 3 5% 6% 64%	1949
	21st to end	Day	3 3 1 2 2 3 3 3 4 7% 68%	1650
March	1st to 10th	Day	2 2 1 3 3 2 3 3 5% 8% 67%	4500
	11th to 20th	Day	4 2 1 2 2 2 3 2 4 6% 71%	4972
	21st to end	Day	2 3 1 3 3 3 3 4 6% 8% 65%	5870
April	1st to 10th	Day	3 2 1 2 3 3 3 3 5% 6% 70%	2400
	11th to 20th	Day	2 3 1 3 2 2 3 3 4 6% 72%	2371
	21st to end	Day	3 2 1 2 2 2 2 2 4 6% 74%	2400
May	1st to 10th	Day	2 2 1 2 2 2 2 2 2 4 82%	5440
	11th to 20th	Day	2 1 1 3 2 3 3 3 5% 7% 70%	5405
	21st to end	Day	2 1 1 2 2 2 2 3 4 5% 76%	5944
June	1st to 10th	Day	1 1 2 2 2 3 3 5% 9% 73%	2507
	11th to 20th	Day	2 2 1 2 2 2 3 3 5% 7% 71%	2499
	21st to end	Day	2 3 1 3 3 3 4 4 6% 8% 62%	2400
July	1st to 10th	Day	3 2 1 3 3 4 5% 4 7% 9% 59%	5439
	11th to 20th	Day	2 1 1 2 2 2 4 4 8% 11% 63%	5440
	21st to end	Day	2 2 1 3 3 4 5% 5% 8% 11% 57%	5922
August	1st to 10th	Day	1 1 1 2 2 3 3 4 6% 10% 69%	5348
	11th to 20th	Day	2 2 1 3 3 4 5% 5% 7% 12% 57%	5366
	21st to end	Day	2 2 1 3 3 4 4 5% 6% 10% 61%	5984
September	1st to 10th	Day	6% 5% 2 5% 4 4 4 4 6% 9% 51%	2400
	11th to 20th	Day	7% 4 2 5% 3 3 4 4 6% 8% 54%	2301
	21st to end	Day	5% 3 1 4 3 3 3 4 6% 7% 61%	2200
October	1st to 10th	Day	1 1 1 2 2 2 2 3 4 81%	3590
	11th to 20th	Day	3 2 1 2 2 2 2 3 3 5% 75%	3299
	21st to end	Day	2 2 1 1 1 1 1 1 2 3 84%	3548
November	1st to 10th	Day	4 3 2 2 2 2 3 2 3 4 73%	2059
	11th to 20th	Day	3 3 1 3 2 3 3 3 4 6% 70%	1937
	21st to end	Day	5% 4 2 4 3 4 3 3 4 6% 62%	1890
December	1st to 10th	Day	5% 6% 1 4 3 3 4 3 6% 8% 57%	3030
	11th to 20th	Day	1 3 1 4 3 3 4 3 4 6% 66%	3454
	21st to end	Day	2 2 1 3 2 3 2 2 5% 6% 72%	4966
January	1st to 10th	Night	3 2 1 2 1 1 2 2 4 8% 74%	5428
	11th to 20th	Night	3 2 2 2 2 2 2 4 5% 76%	5440
	21st to end	Night	4 4 1 4 3 3 3 3 5% 7% 62%	5984
February	1st to 10th	Night	4 3 1 4 2 3 3 3 4 8% 65%	2400
	11th to 20th	Night	4 4 2 4 3 3 4 3 5% 8% 60%	2338
	21st to end	Night	4 3 1 3 3 2 4 3 6% 7% 63%	1980
March	1st to 10th	Night	2 3 1 4 3 3 4 2 4 9% 65%	5374
	11th to 20th	Night	5% 3 1 2 2 2 2 2 4 6% 71%	5010
	21st to end	Night	4 4 1 3 3 3 3 3 5% 6% 65%	5086
April	1st to 10th	Night	4 3 1 4 3 3 4 3 5% 5% 66%	2000
	11th to 20th	Night	3 3 1 3 3 2 4 3 5% 7% 65%	1977
	21st to end	Night	3 3 1 3 2 2 3 3 3 6% 72%	2000
May	1st to 10th	Night	2 1 1 2 1 2 2 2 3 4 80%	4540
	11th to 20th	Night	6% 3 1 4 3 3 4 4 5% 6% 60%	4510
	21st to end	Night	4 2 1 3 3 3 3 4 5% 8% 64%	4953
June	1st to 10th	Night	2 2 1 4 4 4 5% 5% 10% 11% 53%	1871
	11th to 20th	Night	3 2 2 4 5% 5% 5% 5% 6% 11% 52%	1876
	21st to end	Night	3 4 1 4 5% 4 5% 4 8% 10% 51%	2000
July	1st to 10th	Night	3 3 2 5% 4 5% 5% 5% 7% 11% 49%	4540
	11th to 20th	Night	2 2 1 4 3 4 5% 5% 7% 13% 55%	4540
	21st to end	Night	2 3 2 5% 6% 5% 7% 6% 8% 11% 46%	4951
August	1st to 10th	Night	1 1 1 3 3 3 4 4 7% 10% 61%	4464
	11th to 20th	Night	2 2 1 4 4 5% 6% 6% 9% 14% 48%	4483
	21st to end	Night	2 2 1 4 3 4 6% 5% 9% 12% 53%	4993
September	1st to 10th	Night	5% 6% 2 6% 4 4 6% 5% 6% 8% 47%	2000
	11th to 20th	Night	5% 4 2 6% 5% 6% 6% 6% 8% 10% 42%	2096
	21st to end	Night	4 3 2 5% 5% 4 5% 5% 7% 9% 51%	2200
October	1st to 10th	Night	1 2 1 3 2 2 3 2 4 5% 75%	3590
	11th to 20th	Night	4 3 1 4 3 3 2 2 4 6% 68%	3829
	21st to end	Night	2 1 1 1 1 1 1 2 3 4 82%	4252
November	1st to 10th	Night	5% 2 1 2 1 2 2 2 3 3 77%	2460
	11th to 20th	Night	3 3 1 3 2 3 3 3 5% 6% 70%	2657
	21st to end	Night	4 3 1 3 3 3 3 3 4 6% 66%	2730
December	1st to 10th	Night	6% 4 1 5% 4 4 4 4 6% 7% 56%	4380
	11th to 20th	Night	2 3 1 3 2 2 2 3 4 6% 72%	4908
	21st to end	Night	2 2 1 3 2 2 3 2 5% 7% 71%	6050

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	8% 27% 3 17% 24% 21%	4538
	11th to 20th	Day	8% 26% 3 14% 29% 21%	4540
	21st to end	Day	14% 29% 3 18% 22% 14%	4994
February	1st to 10th	Day	9% 62% 2 5% 9% 14%	2000
	11th to 20th	Day	8% 61% 3 7% 10% 11%	1959
	21st to end	Day	7% 62% 1 4 11% 15%	1650
March	1st to 10th	Day	12% 29% 3 8% 16% 33%	4500
	11th to 20th	Day	9% 29% 3 7% 15% 36%	4972
	21st to end	Day	12% 29% 3 6% 20% 30%	5870
April	1st to 10th	Day	7% 61% 2 4 10% 17%	2400
	11th to 20th	Day	7% 62% 2 5% 8% 14%	2374
	21st to end	Day	6% 61% 2 5% 10% 16%	2400
May	1st to 10th	Day	5% 28% 1 6% 16% 44%	5440
	11th to 20th	Day	10% 28% 4 7% 20% 32%	5408
	21st to end	Day	7% 28% 5% 10% 14% 35%	5945
June	1st to 10th	Day	5% 62% 4 11% 11% 8%	2507
	11th to 20th	Day	5% 61% 3 7% 11% 12%	2499
	21st to end	Day	7% 61% 6% 9% 10% 8%	2400
July	1st to 10th	Day	13% 28% 13% 22% 18% 5%	5381
	11th to 20th	Day	8% 28% 15% 32% 14% 3	5377
	21st to end	Day	12% 28% 13% 19% 21% 7%	5752
August	1st to 10th	Day	9% 37% 6% 21% 19% 8%	3892
	11th to 20th	Day	8% 38% 10% 23% 16% 5%	3882
	21st to end	Day	10% 38% 9% 21% 17% 5%	4311
September	1st to 10th	Day	12% 57% 6% 10% 8% 7%	2400
	11th to 20th	Day	10% 58% 7% 10% 10% 5%	2301
	21st to end	Day	11% 58% 4 12% 11% 4	2200
October	1st to 10th	Day	4 35% 3 7% 17% 34%	3590
	11th to 20th	Day	7% 36% 6% 14% 12% 26%	3299
	21st to end	Day	5% 34% 1 6% 30% 23%	3548
November	1st to 10th	Day	13% 53% 4 8% 10% 13%	2059
	11th to 20th	Day	11% 55% 5% 11% 10% 9%	1937
	21st to end	Day	11% 54% 4 9% 13% 8%	1890
December	1st to 10th	Day	16% 37% 6% 17% 16% 9%	3030
	11th to 20th	Day	12% 31% 4 16% 28% 9%	3452
	21st to end	Day	8% 27% 3 13% 28% 22%	4966
January	1st to 10th	Night	8% 25% 2 11% 32% 21%	5428
	11th to 20th	Night	8% 26% 3 12% 20% 31%	5440
	21st to end	Night	14% 29% 4 14% 23% 16%	5984
February	1st to 10th	Night	6% 61% 2 6% 10% 14%	2400
	11th to 20th	Night	9% 60% 3 6% 11% 11%	2338
	21st to end	Night	8% 62% 2 5% 9% 14%	1980
March	1st to 10th	Night	14% 29% 2 6% 15% 34%	5374
	11th to 20th	Night	9% 30% 4 8% 15% 34%	5010
	21st to end	Night	15% 30% 3 5% 14% 33%	5086
April	1st to 10th	Night	7% 62% 2 4 9% 17%	2000
	11th to 20th	Night	8% 63% 3 5% 6% 15%	1977
	21st to end	Night	7% 61% 2 5% 10% 14%	2000
May	1st to 10th	Night	5% 27% 3 8% 15% 42%	4537
	11th to 20th	Night	16% 28% 5% 7% 12% 32%	4511
	21st to end	Night	12% 29% 5% 11% 12% 30%	4954
June	1st to 10th	Night	9% 64% 4 9% 10% 4	1871
	11th to 20th	Night	9% 62% 3 7% 11% 8%	1876
	21st to end	Night	10% 60% 7% 9% 8% 7%	2000
July	1st to 10th	Night	20% 29% 14% 21% 14% 2	4490
	11th to 20th	Night	14% 28% 13% 28% 14% 3	4480
	21st to end	Night	19% 28% 12% 17% 18% 6%	4808
August	1st to 10th	Night	11% 37% 6% 19% 23% 5%	3244
	11th to 20th	Night	11% 38% 10% 24% 14% 4	3243
	21st to end	Night	12% 38% 11% 21% 15% 3	3597
September	1st to 10th	Night	13% 58% 6% 9% 7% 6%	2000
	11th to 20th	Night	15% 60% 5% 8% 7% 5%	2096
	21st to end	Night	13% 59% 6% 10% 9% 4	2200
October	1st to 10th	Night	7% 36% 4 5% 13% 36%	3590
	11th to 20th	Night	9% 35% 6% 10% 10% 29%	3829
	21st to end	Night	5% 35% 2 8% 28% 22%	4252
November	1st to 10th	Night	10% 54% 4 7% 10% 14%	2460
	11th to 20th	Night	11% 55% 3 10% 11% 10%	2657
	21st to end	Night	9% 53% 4 8% 14% 11%	2730
December	1st to 10th	Night	20% 36% 5% 15% 13% 12%	4380
	11th to 20th	Night	9% 31% 3 13% 28% 16%	4909
	21st to end	Night	9% 27% 3 10% 33% 18%	6050

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	7% 3 18% 40% 26% 5%	300
	11th to 20th	Day	3 5% 16% 45% 27% 4	300
	21st to end	Day	2 6% 22% 41% 25% 4	330
February	1st to 10th	Day	8% 4 15% 33% 30% 11%	300
	11th to 20th	Day	8% 6% 17% 43% 23% 3	300
	21st to end	Day	5% 7% 23% 45% 19% 2	249
March	1st to 10th	Day	9% 5% 17% 46% 20% 3	300
	11th to 20th	Day	8% 10% 25% 32% 19% 5%	485
	21st to end	Day	4 13% 21% 38% 21% 2	550
April	1st to 10th	Day	6% 8% 25% 39% 20% 3	500
	11th to 20th	Day	3 12% 27% 37% 17% 4	492
	21st to end	Day	5% 7% 22% 44% 22% 1	500
May	1st to 10th	Day	3 7% 21% 42% 21% 5%	503
	11th to 20th	Day	3 6% 22% 40% 25% 5%	528
	21st to end	Day	3 3 18% 39% 34% 4	573
June	1st to 10th	Day	2 1 10% 35% 39% 12%	637
	11th to 20th	Day	2 1 7% 29% 45% 15%	629
	21st to end	Day	2 1 7% 30% 36% 24%	530
July	1st to 10th	Day	4 6% 21% 31% 37%	526
	11th to 20th	Day	2 3 22% 34% 39%	524
	21st to end	Day	2 1 3 24% 38% 32%	575
August	1st to 10th	Day	2 1 4 17% 35% 42%	527
	11th to 20th	Day	5% 1 5% 20% 32% 38%	517
	21st to end	Day	4 1 5% 21% 31% 38%	583
September	1st to 10th	Day	7% 2 6% 25% 33% 28%	530
	11th to 20th	Day	7% 1 4 17% 39% 34%	431
	21st to end	Day	7% 1 5% 17% 37% 34%	330
October	1st to 10th	Day	3 2 5% 21% 36% 34%	330
	11th to 20th	Day	6% 2 9% 24% 32% 27%	330
	21st to end	Day	4 3 9% 25% 34% 25%	363
November	1st to 10th	Day	3 3 8% 29% 39% 18%	330
	11th to 20th	Day	4 6% 9% 29% 34% 18%	330
	21st to end	Day	8% 4 15% 34% 31% 8%	330
December	1st to 10th	Day	6% 3 8% 35% 36% 12%	330
	11th to 20th	Day	3 3 16% 38% 32% 9%	321
	21st to end	Day	5% 3 15% 41% 31% 5%	330
January	1st to 10th	Night	6% 3 23% 51% 18%	800
	11th to 20th	Night	8% 3 21% 50% 18%	800
	21st to end	Night	6% 4 28% 49% 12%	880
February	1st to 10th	Night	5% 5% 26% 46% 19%	800
	11th to 20th	Night	7% 6% 28% 49% 10%	784
	21st to end	Night	5% 6% 35% 48% 5%	660
March	1st to 10th	Night	8% 6% 34% 44% 8%	800
	11th to 20th	Night	9% 7% 34% 39% 12%	800
	21st to end	Night	5% 6% 35% 45% 9%	710
April	1st to 10th	Night	4 7% 39% 45% 6% 1	600
	11th to 20th	Night	4 8% 40% 42% 6%	593
	21st to end	Night	4 7% 40% 45% 5%	600
May	1st to 10th	Night	5% 7% 37% 43% 8%	600
	11th to 20th	Night	6% 5% 35% 47% 8% 1	591
	21st to end	Night	4 5% 31% 50% 10%	650
June	1st to 10th	Night	3 2 25% 57% 15%	600
	11th to 20th	Night	3 1 22% 53% 21%	600
	21st to end	Night	3 2 18% 56% 21% 1	600
July	1st to 10th	Night	3 1 12% 51% 30% 2	585
	11th to 20th	Night	4 2 7% 54% 32% 1	582
	21st to end	Night	3 2 6% 50% 36% 3	657
August	1st to 10th	Night	3 1 6% 44% 44% 3	597
	11th to 20th	Night	5% 1 5% 40% 43% 5%	594
	21st to end	Night	4 1 6% 48% 37% 3	660
September	1st to 10th	Night	5% 2 10% 48% 33% 2	600
	11th to 20th	Night	7% 1 11% 50% 31% 1	600
	21st to end	Night	4 1 12% 51% 30% 2	600
October	1st to 10th	Night	3 1 12% 58% 25% 1	600
	11th to 20th	Night	7% 2 19% 46% 25% 2	757
	21st to end	Night	4 2 16% 46% 29% 3	880
November	1st to 10th	Night	6% 1 13% 46% 32% 2	820
	11th to 20th	Night	4 4 14% 52% 25% 1	977
	21st to end	Night	6% 2 21% 51% 19% 2	1050
December	1st to 10th	Night	7% 3 15% 53% 21% 1	1050
	11th to 20th	Night	4 2 21% 52% 20% 1	1036
	21st to end	Night	5% 2 22% 53% 17% 1	907

Page generated at 2025-12-15 00:13:50. Version ac07

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